The Body Snatchersis a 1955 sciencefiction novel by Jack Finney, originally serialized in Colliers Magazine in 1954, which describes the town of Mill Valley, California, being invaded by seeds that have drifted to Earth from space. The seeds replace sleeping people with perfect physical duplicates grown from plantlike pods, while their human victims turn to dust. The duplicates live only five years, and they cannot sexually reproduce; consequently, if unstopped, they will quickly turn Earth into a dead planet and move on to the next world. One of the duplicate invaders suggests that this is what all humans do; use up resources, wipe out indigenous populations, and destroy ecosystems in the name of survival.

The novel has been adapted for the screen four times; the first film in 1956, the second in 1978, the third in 1993, and the most recent in 2007. Unlike two of the film adaptations, the novel contains an optimistic ending, with the aliens voluntarily vacating after deciding that they cannot tolerate the type of resistance they see in the main characters.

are a group of animals that includes mammals and every animal more closely related to mammals than to other living amniotes. They are easily separated from other amniotes by having a temporal fenestra, an opening low in the skull roof behind each eye, leaving a bony arch beneath each; this accounts for their name. Primitive synapsids are usually called pelycosaurs or pelycosaur-grade synapsids; more advanced mammal-like ones, therapsids. The non-mammalian members are described as mammal-like reptiles in classical systematics; they can also be called stem mammals or proto-mammals. Synapsids evolved from basal amniotes and are one of the two major groups of the later amniotes; the other is the sauropsids, a group that includes modern reptiles and birds. The distinctive temporal fenestra developed in the ancestral synapsid about 312 million years ago, during the Late Carboniferous period. Synapsids were the largest terrestrial vertebrates in the Permian period, 299 to 251 million years ago, although some of the larger pareiasaurs
at the end of Permian could match them in size. As with other groups
then extant, their numbers and variety were severely reduced by the Permian–Triassic extinction. By the time of the extinction at the end of Permian, all the older forms of synapsids (known as pelycosaurs) were already gone, having been replaced by the more advanced therapsids. Though the dicynodonts and Eutheriodontia, the latter consisting of Eutherocephalia (Therocephalia) and Epicynodontia (Cynodontia), continued into the Triassic period as the only known surviving therapsids, archosaurs became the largest and most numerous land vertebrates in the course of this period. The cynodont group Probainognathia, which includes Mammaliaformes, were the only synapsids who outlasted the Triassic. After the Cretaceous–Paleogene extinction event, the synapsids (in the form of mammals) again became the largest land animals.